Plants are known for treating and conditioning various types of products by application and use of alternate electromagnetic fields having various frequencies.
Particularly, plants are known which operate using electromagnetic fields operating in the microwave or radio-frequency range, and used for drying relatively wet products, such as hides or painted products.
Electromagnetic fields are further used in the food processing industry, e.g. for pasteurization of products containing milk or eggs products and in general for conditioning and/or sanitization treatment of any food product.
The applicant hereof manufactures and sells a treatment plant which uses an alternate radio-frequency electromagnetic field, such plant basically comprising a voltage generator that supplies voltage to an applicator having a pair of electrodes for producing the electromagnetic field through which the products to be treated are designed to pass.
The applicator further comprises a capacitor, which is electrically connected to the electrodes and has a pair of opposed plates. The distance between the plates may be mechanically adjusted to vary the capacitance of the capacitor, thereby varying the supply voltage to the electrodes and, accordingly, the electromagnetic field emission power.
With power adjustment, the heating temperature generated by the electromagnetic field on the products to be treated may be varied.
While this solution has shown remarkable effectiveness and reliability, it is still susceptible of improvement, namely concerning regulation of the electromagnetic field power.
The mechanical movement of the plates of the capacitor for varying the field power has relatively long response times, which do not allow instantaneous operating temperature adaptation.
U.S. Pat. No. 2,640,908, which represents the closest prior art, discloses an oscillator which comprises a pair of triodes having the characteristics of the preamble of claim 1.